In view of protecting the environment, fuel vapor has been controlled as well as the exhaust emission control. According to the regulation established by the Environmental Protection Agency (EPA) and the California Air Resourced Board (CARB), a leak detection of the fuel vapor from a fuel tank is required.
A conventional leak check system shown in JP-10-90107A, which is a counterpart of U.S. Pat. No. 5,890,474, has a pump which generate a pressure gradient between an inside and an outside of a fuel tank. When a leakage of fuel vapor from the fuel tank, a load of a motor driving the pump fluctuates. The detection of fuel vapor leakage is conducted by checking the fluctuation of the motor load.
However, because the motor load is detected based on current and voltage supplied thereto, fluctuation of the voltage and an atmospheric temperature around the motor may affect an accuracy of the detection of fuel vapor leakage. In order to improve the accuracy, JP-2003-90270A, which is a counterpart of US application Publication 2003/0051541A1, shows a fuel vapor leak check system which has a pressure sensor sensing an inner pressure of the fuel tank.
A pressure of air, which is induced to and discharged form the pump, fluctuates periodically. When the pressure sensor is disposed near the inlet and the outlet of the pump, a sensing accuracy of the pressure sensor is deteriorated.